1. Field of the Invention
This invention relates to grinding machines with expansible grinding tools and in particular to devices for controlling the expansion of the grinding tool.
2. Description of the Prior Art
Expansible grinding tools are used, for example, in the machining of internal bores and grinding machines using such tools comprise means for rotating the tool and a device for controlling the expansion of the tool. The tools themselves comprise in the majority of cases abrasive stones, or diamonds, disposed around the periphery of a support cylinder and able to move radially under the action of axial movement of a cone in the support cylinder. Such movement of the cone can, for example, be effected by a rod integral with the cone and fast for translational movement with a screw engaged with a fixed nut and rotatable via a reduction gear train by a driving motor. In known grinding machines the whole of the expansion control mechanism is carried directly by the frame of the machine. The mounting of the driving motor of the expansion screw on the machine frame makes it necessary to provide a sliding connection between the shaft of the motor and the screw. Moreover, when a breakdown occurs in the expansion control mechanism, the grinding machine becomes unusable until the expansion control mechanism has been repaired.